First of all, many thanks for all of the good people that has been contributing here.
I got here about a year ago via Google search and was able to fix a malfunctioning LCD monitor by replacing some swollen caps, following just the advice I read here, with no need to bother any of you :)

I have now on my hands a malfunctioning Philips LCD TV, model 42PFL5322/10 with a 42" AUO 1366x768 LCD panel.

Symptoms: after turning set on, image shows up within about 4secs, then the display shuts down about 2secs later (with backlight turned off as well) and remains off till the next time the TV set is turned off and back on. After the display shuts down, sound still audible, and I can't seem to see anything if I shine a light on the screen.

I thought I'd be able to easily fix it as I did with the other monitor a year ago, but this time I can't see any obviously malfunctioning capacitor.
A certain capacitor has a radioactive-yellow tint on its top, but it looks to me like it was simply marked with a highlighting marker.
Also, some caps are mounted under enclosing metal plates which prohibit me from examining the caps properly. Looking from the side they look OK, but I might be wrong. The plates are a PITA to take off as they are soldered and also have some components externally stuck to them (to be used as a heatsink, I reckon).

I went ahead and downloaded the service manual, which unfortunately includes schemes for the SSB board only, with no schemes for neither the PSU, nor the inverter boards.

Some voltage and control lines I went through all showed voltages well within the range specified in the manual, these lines are labeled "+12v_disp", "+5v_standby", "+5V_SW", "+3V3_SW".

Also, control lines labeled "BL_ON_OFF" and "VDISP" show what appears to be a normal behaviour, meaning they go active about 4secs after I turn the set on, and remain active for as long as it is on, even though the display shuts down 2secs later.

I can order a replacement PSU on eBay, but I'm not sure if this is where the problem's at. From the control line behaviour I tend to believe the fault might be with the inverters.

Many thanks in advance for any advice/opinion.

I've attached pics of the set, various close ups, including of the capacitor with the radioactive-yellow marking.

sagie

11-16-2011 05:52 PM

Re: Philips LCD TV with Sound, No Picture (model 42PFL5322/10)

I forgot to write that as the TV is turned on, the red standby LED changes to a blue LED, which remains on as long as the TV is on (regardless whether the display works or not).
When the TV is turned off the blue LED changes to back to the red standby LED.

No LED blinking at any point, except as a feedback when I use the remote.

retiredcaps

11-16-2011 06:32 PM

Re: Philips LCD TV with Sound, No Picture (model 42PFL5322/10)

Quote:

Originally Posted by sagie
(Post 196849)

I can order a replacement PSU on eBay, but I'm not sure if this is where the problem's at. From the control line behaviour I tend to believe the fault might be with the inverters.

2 seconds to black can be

a) bad caps
b) bad ccfls and/or wiring
c) bad inverter transformer

a) It looks like all Rubycon caps and Rubycon has a good reputation for reliability so we will assume they are good for now.

b) A single bad ccfl or wiring can cause the inverter circuitry to go into protection mode and shut down all the ccfls.

c) Let's focus here first. There seems to be 10 inverter transformers on either side of the TV. You will have to measure the resistance of secondary pins for each of the 20 inverters. If there is a part number, report it.

All 20 should read within 3% of each other. If not, you have a bad inverter transformer. If you need help identifying which are the correct pins, take a clear close up picture of a couple of them (just 2 is the picture).

2 seconds to black is discussed in more detail at (starting with posts #13 and #14)

I've read some similar text here at the forum, but I wasn't sure whether this was applicable to my situation since I can't see any picture when I shine a light on the screen. Does this makes any difference?

Thanks again!

retiredcaps

11-16-2011 07:37 PM

Re: Philips LCD TV with Sound, No Picture (model 42PFL5322/10)

Quote:

Originally Posted by sagie
(Post 196879)

Do I have to take the transformers out of the circuit to measure the resistance, or may I measure it in-circuit?

You can measure them "in circuit". List all your measurements for all inverter transformers.

Quote:

I've read some similar text here at the forum, but I wasn't sure whether this was applicable to my situation since I can't see any picture when I shine a light on the screen. Does this makes any difference?

Sometimes the flashlight trick doesn't work because of the screen, material, angle, etc. If you look in a dark room, you may have better luck?

It just takes one of the 20 inverter transformers to fail and the whole thing will shut down.

sagie

11-16-2011 07:37 PM

Re: Philips LCD TV with Sound, No Picture (model 42PFL5322/10)

Quote:

Originally Posted by sagie
(Post 196879)

Do I have to take the transformers out of the circuit to measure the resistance, or may I measure it in-circuit?

OK, I've just read in the article you've linked I can measure it in-circuit.

Only one question remains -

Quote:

Originally Posted by sagie
(Post 196879)

I wasn't sure whether this was applicable to my situation since I can't see any picture when I shine a light on the screen. Does this makes any difference?

Thanks again!

sagie

11-16-2011 07:40 PM

Re: Philips LCD TV with Sound, No Picture (model 42PFL5322/10)

Quote:

Originally Posted by retiredcaps
(Post 196881)

You can measure them "in circuit". List all your measurements for all inverter transformers.

Sometimes the flashlight trick doesn't work because of the screen, material, angle, etc. If you look in a dark room, you may have better luck?

It just takes one of the 20 inverter transformers to fail and the whole thing will shut down.

I tried to look in various lighting conditions, but I'll give the transformers a shot. Will update with my results.
Thanks!

sagie

11-17-2011 06:37 AM

Re: Philips LCD TV with Sound, No Picture (model 42PFL5322/10)

Quote:

Originally Posted by retiredcaps
(Post 196856)

c) Let's focus here first. There seems to be 10 inverter transformers on either side of the TV. You will have to measure the resistance of secondary pins for each of the 20 inverters. If there is a part number, report it.

All 20 should read within 3% of each other. If not, you have a bad inverter transformer. If you need help identifying which are the correct pins, take a clear close up picture of a couple of them (just 2 is the picture).

OK, the transformers are all 4004Qs. I tested all 40 secondary winding pairs, they all measure in the range of 1310-1360 Ohm. Went ahead and tested the 20 primary winding pairs, they all measure in the range of 1.1 - 1.6 Ohm.

I'm assuming my readings indicate the transformers are OK. Can anybody offer some more advice?

Many thanks!

retiredcaps

11-17-2011 03:23 PM

Re: Philips LCD TV with Sound, No Picture (model 42PFL5322/10)

Quote:

Originally Posted by sagie
(Post 196945)

I tested all 40 secondary winding pairs, they all measure in the range of 1310-1360 Ohm.

Can you actually list all 40 readings? It matters because if 39 of them measure between 1350-1360 Ohm and 1 reads 1310 Ohm, then

edit: We have had cases where the measurement was off by as little as 5 Ohms to cause "2 seconds to black".

OK, as I checked the resistances a second time to write them down, I got much more consolidated readouts for some reason. This time, they were all in the range of 1300-1333 Ohms, which makes the max reading still within 3% from the min reading. I wrote all of the readings in the bottom of this message.

Quote:

Originally Posted by retiredcaps
(Post 197030)

Are there any caps on the inverter board? If yes, what brand and series are they?

Yes, each of the 2 boards carries 5 medium sized caps and a small cap. They all appear to be in good shape visually (at least in my eyes).

I couldn't really make a brand, but here are the markings on them:
* Medium sized - 1st type

(M)105°C
7(7)
1W

* Medium sized - 2nd type

(M)105°C
7(7)
3W

* Small sized - 3rd type

(M)105°C

One of the boards carries 5 caps of the 1st type and 1 of the 3rd. The other board carries 3 caps of the 1st type, 2 of the 2nd and 1 of the 3rd.
I think the manufacturer simply uses the 1st and 2nd types interchangeably.

I've also attached some photos to show the one of the boards and a few of the caps.

This time, they were all in the range of 1300-1333 Ohms, which makes the max reading still within 3% from the min reading.

Those readings suggest the inverter transformers are likely good.

Quote:

Yes, each of the 2 boards carries 5 medium sized caps and a small cap.

The Mercedes Benz vent and the brown color suggest they are United Chemi-con caps. UCC is a reliable manufacturer, but they have a problematic series with the KZG caps.

Assuming the caps are good on the inverter board and power board, that leaves the ccfls and/or wiring to check.

I'm not sure how to test the 20 ccfls. I'll have to think and do some searching.

sagie

11-18-2011 08:15 PM

Re: Philips LCD TV with Sound, No Picture (model 42PFL5322/10)

Thanks again for your help, retiredcaps.

Quote:

Originally Posted by retiredcaps
(Post 197271)

I'm not sure how to test the 20 ccfls. I'll have to think and do some searching.

I might save you some searching by telling you the service manual which is widely available on the Internet for this chassis (LC7.1E LA) has absolutely no information about neither the CCFLs, nor the PSU or the inverter boards, so there is no specification for spare CCFLs, etc. It appears to me as if Philips has no interest in having these parts being serviced.

I might save you some searching by telling you the service manual which is widely available on the Internet for this chassis (LC7.1E LA) has absolutely no information about neither the CCFLs, nor the PSU or the inverter boards, so there is no specification for spare CCFLs, etc. It appears to me as if Philips has no interest in having these parts being serviced.

It's not a matter of interest, it's a matter of ability. The following applies to both LCD and plasma, (and to a certain extent, even DLP) TVs.

There are only a few companies making flat panels. When Philips wants to build an LCD TV, they purchase LCD assemblies from one of the LCD panel manufacturers. The LCD assembly consists of the LCD panel, the inverter(s), the CCFLs, and the tcon. The power supply may be a similar situation - they purchase them from a manufacturer. In the case of a plasma panel, the panel, sustains, buffers, main control card, and often the power supply are sold as a unit.

Philips is quite good about providing schematics where possible, but if the subassembly is built by another firm, they are usually unable to provide schematics.

PlainBill

Huttonfrank

11-20-2011 11:59 AM

Re: Philips LCD TV with Sound, No Picture (model 42PFL5322/10)

I am trying to repair a LG 32LC56. It has a single inverter board very similar to this one. (mine is VIT71020.66 MODULE INVERTER V.32 LCD-TV REF : 19.31T03.001) There are only six CCFLs. I have established that Philips and LG have a lot of common parts.
Symptoms are the same. On the inverter board is an IC type OZ964. The data sheet is free on the net. It is a DC/AC CCFL generator and control IC.
The application circuit shown is only for 1 CCFL so in this case the circuitry is much more extensive. I found that pin 3 of the OZ964 which is the enable pin goes from 5V when the backlight is on to 0v when it goes off. the line from the pin goes to various other points on the board, so it seems that an over or under voltage or current detection circuit is driving this line low and shutting down the CCFLs.
One of the transformer secondaries is 732 ohms, whereas the other 5 are 767 - 782 ohms. So there may be short circuit turns on this one. BUT even if I can prove it is the fault where could I get a replacement?

retiredcaps

11-20-2011 03:16 PM

Re: Philips LCD TV with Sound, No Picture (model 42PFL5322/10)

Quote:

Originally Posted by Huttonfrank
(Post 197620)

One of the transformer secondaries is 732 ohms, whereas the other 5 are 767 - 782 ohms. So there may be short circuit turns on this one. BUT even if I can prove it is the fault where could I get a replacement?

Well, looks like I fixed it. It wasn't the CCFLs, but the ingenuously simple CCFL test helped me find the problem. From the CCFL test I detected what appeared to be two malfunctioning CCFLs. The two were next to each other, in one corner of the set.

It seemed to me too much of a coincidence that 2 adjacent CCFLs failed together. So I searched the power supply path of the 2 CCFLs for shared components that could've failed. I found out the 2 were sharing an SMT 3A fuse. I tested its resistance, and unsurprisingly, it wasn't conducting. I soldered a new 3A fuse, and the set now works.

Many thanks for your help, retiredcaps and PlainBill!

retiredcaps

11-20-2011 05:33 PM

Re: Philips LCD TV with Sound, No Picture (model 42PFL5322/10)

Quote:

Originally Posted by sagie
(Post 197691)

I found out the 2 were sharing an SMT 3A fuse. I tested its resistance, and unsurprisingly, it wasn't conducting.

Great job of tracking that down. Ironically, a bad fuse is mentioned in the 2 seconds to black guide, but I haven't mentioned it as a possible cause for a while now.

Anyway, thanks for the following up and getting your TV working again.